Lunar Prospector

Lunar Prospector was the first competitively selected and third to launch in a series of missions in NASA's Discovery program. This program was developed to produce frequent, low-cost missions to explore the Solar System. Lunar Prospector was a simple and reliable spin-stabilized spacecraft that rotated around its own central axis in order to control its orientation en route to the Moon. Prospector was small -- when full of fuel, the spacecraft weighed only 295 kg (650 lb). That's about a quarter as heavy as an average-sized car! It carried a small payload of only five instruments.

Water on the moon?
In 1998, the Lunar Prospector used a device called a neutron spectrometer to scan the Moon's surface for hydrogen-rich minerals. Once again, polar craters yielded an intriguing signal: neutron ratios indicated hydrogen. Many scientists believe this is evidence of possible water ( H2O) on the moon.

Like all Discovery missions, Prospector progressed rapidly from development to completion an testing phases -- the entire process was accomplished in a period of only 22 months. One of the features that speeded the process along is the fact that, where feasible, the spacecraft was manufactured from "off-the-shelf," flight-proven hardware. From an engineering perspective, a spin-stabilized spacecraft like Prospector is inexpensive to design and simple to operate. During its one-year polar orbiting mission, Lunar Prospector had the exciting and exacting task of sleuthing some of the Moon's remaining mysteries, including whether or not water ice is buried inside the lunar crust. Besides water, Lunar Prospector looked for other natural resources, such as minerals and gases, that could be used to build and sustain a future human lunar base or in manufacturing fuel for launching spacecraft from the Moon to the rest of the Solar System.

Lunar Prospector, using its Gamma Ray Spectrometer, collected a large amount of scientific data that helped researchers understand the chemical composition of the lunar surface. Some of the spacecraft's prospecting tools, or scientific instruments, also measured the Moon's magnetic and gravitational fields, enhancing our current understanding as well as potentially enabling future mission scientists to design more fuel-efficient journeys to the Moon. In addition, Prospector carried a special instrument, called an Alpha Particle Spectrometer, that sniffed out small quantities of gases that leak out from the lunar interior. Collectively, the scientific data that Prospector sent back to Earth helped researchers construct a more complete and detailed map of our nearest planetary neighbor, the Moon.

The mission found evidence of water ice in shadowed craters near the lunar poles, a key issue for any future human exploration. LP was launched 1998 January 6, and made a planned crash into the moon on 1999 July 31.